Method for extracting iron by direct reduction

ABSTRACT

The invention relates to a method and a device for extracting iron by direct reduction, characterized in that the device has a separate reduction chamber in which the carbon is gasified and the iron oxide is reduced in close proximity, and a separate combustion chamber in which surplus reduction gases are burned and heat energy is yielded. According to the invention, the hot combustion gasses pass on their heat energy to the reduction gasses in a heat exchanger, so that this energy is transferred to the reduction gases effectively. The reduction gasses are force-circulated through the heat exchanger and through the carbon/bed of ore for this purpose.

BACKGROUND OF THE INVENTION

The present invention relates to a method and a device for the directreduction of iron ore with coal.

Such methods and devices are employed in the production of iron or steelfrom iron ore, ie in metallurgy for example.

The methods applied for by far the greatest part of iron production fromore utilise the carbon in coal or coke for two processes which proceedsimultaneously.

Carbon acts first of all as a chemical reducing agent and takes over theoxygen from the iron oxide.

Secondly, by combustion with oxygen (usually from the air) carbonsupplies the necessary heat for the process.

For the best utilisation of the coal each of these two process stepsrequires thermodynamic conditions which are mutually exclusive(“thermodynamic dilemma”).

For the reduction, the chemical potential of the oxygen in theatmosphere must be as low as possible, ie high CO content, low CO₂content and low O₂ content in equilibrium with CO.

For the most complete possible combustion of the carbon to CO₂, an O₂content in the combustion atmosphere meeting at least the stoichiometricrequirements is needed.

In the coal reduction methods currently used in industry compromises areentered into. Accordingly, more energy is expended than is needed forthe actual iron ore production process. At the same time the methodsresult either in reduction gas which does not have the full capabilityfor reducing the oxide because before it is used for reduction the gashas already taken up oxygen by partial combustion or they result in theheat needed not being produced with optimum efficiency since the gascannot be burned completely to CO₂.

Depending on the process, the unused portion of energy is dissipated inthe form of carbon monoxide and hydrogen or as perceptible heat or both.The more or less advantageous use of the coupled product, energy, fromthese non-autothermic processes has a substantial effect on the economicefficiency of the overall process. In the blast furnace method theexcess energy is given off in chemical form as furnace gas usually tousage loads located in the works. In the case of the rotary-tube furnacemethod the utilisation of the excess energy is difficult becausefrequently no usage loads are available. Occasionally the excess energyis converted to electrical energy.

SUMMARY OF THE INVENTION

In order to improve the energy yield in the context addressed here tworoutes have been taken. The compromise referred to has been improved orprocesses have been proposed which proceed without excess energy and arethus autothermic.

The characteristics of known methods affecting energy demand are hereexamined in more detail and compared.

For this purpose the RIST diagram in FIG. 1 is used. This shows on theabscissa the oxidation of the carbon as the molar ratio from O/C=0 toO/C=2, ie from carbon C to carbon dioxide CO₂, and on the ordinate theorigin of the required oxygen with reference to one mol of Fe and thusexpressed by the molar ratio O/Fe.

This oxygen taken up by the carbon can come from the ore (central regionof the ordinate) or it can be free oxygen for precombustion (lower part)or afterburning (upper part). The terms precombustion and afterburningrefer to the combustion of C or CO before and after, respectively, thesehave been used for reduction.

The removal of oxygen from the oxide illustrating the reduction becomesmore clearly discernible if the number of mols of oxygen present in theoxide in question during the reduction process is always related tob 1mol of iron instead of the conventional 1, 2 or 3 mols of iron. Thefollowing notations then emerge:

haematite, Fe₂O₃, becomes FeO_(1.5);

magnetite, Fe₃O₄, becomes FeO_(1.33); and

wüstite, FeO, becomes FeO_(1.05).

The quantity of oxygen required for the combustion of a portion of thecoal or CO (precombustion/afterburning) is also related to 1 mol ofiron. Precombustion is given a negative sign and is plotted to −1.5. If,for example, 1.5 mols of oxygen/mol of Fe are needed for precombustionthe diagram shows that just as much oxygen for precombustion as forreduction, ie 1.5 mol O per mol Fe in each case and thus 3 O/Fe intotal, is removed from the reactor with the flue gas.

A to D are process lines for different reduction processes. The gradientof a process line, that is the quotient O/Fe/O/C, abbreviates to C/Fethe specific carbon consumption. The latter is particularly importantfor the deliberations pursued here and is specified in the legend of thefigure for the methods under consideration both in terms of mol C/mol Feand kg C/t Fe.

Process line B represents the exchange of oxygen between iron oxide andcarbon as well as the further take up of oxygen by the carbon inafterburning for an ideal autothermic process for the production ofdirectly reduced iron (DRI). The carbon demand is 1.4 mol C per mol Feor 299 kg C/t Fe and is thus almost the lowest possible for a methodbased only on carbon for reduction and heat generation. The diagramshows that the reduction of the iron oxide oxidises the carboncompletely to CO and beyond that converts 10% of it to CO₂. Theremaining gas containing 90% of CO is afterburnt and the heat liberatedcovers the remaining enthalpy requirement of the reaction.

Process line A represents the rotary-tube method. The energy inputrequired is greater than that for an autothermic process as can be seenfrom comparison of the gradients of the process lines. The actual energydemand for reduction in the rotary tube can naturally not be greaterthan that of an autothermic process but as a consequence of the processsubstantially more carbon must be fed in, that is to say 2.1 mol C/molFe, ie 451 kg C/t Fe, so that 152 kg C/t Fe are converted into heat lostin the process. The reason for this is that the CO formed in thereduction reaction must be burnt over the bed of coal and ore in orderto generate the heat required for the Boudouard reaction. Thiscombustion reaction, however, cannot be carried out completely to CO₂because the CO₂ would impair the reduction process. It follows from thisthat any supply of heat without material separation of the gases in thereduction chamber and combustion chamber results for theoretical reasonsin a consumption of carbon and energy which must be higher than that ofa hypothetical autothermic process.

Process line C represents the oxygen exchange in a blast furnaceoperating only with coke. Due to the production of liquid end productsas opposed to solid end products in processes A and B the consumptionvalues have only limited comparability. In the blast furnace bothprecombustion (in the tuyere level) and afterburning (in the air heater)are employed. In the calculation of the carbon consumption the 0.2 C/Fewhich leaves the furnace in the pig iron containing 4.3% C have alreadybe subtracted.

Due to the partial combustion of the carbon in the tuyere level(precombustion) to produce the enthalpy needed for melting and heatingthe charge and for the Boudouard reaction the starting point of theprocess line is lowered by comparison with processes A and B from theorigin of the coordinate system to −1.30 O/Fe. Due to this preliminaryoxidation of the carbon the gas in the upper section of the blastfurnace contains more CO₂ than originates from the reduction reaction.The gas is thus “diluted” with oxygen and is no longer as well suitedfor reducing as it would be without this take-up of oxygen. Accordingly,in contrast with A and B the process line C passes close to the“forbidden region” of the diagram marked by W and M. Since thecompositions of the reducing gas lying in this region no longer resultin the formation of metallic iron a process line cannot run through thiszone.

Since the carbon consumption of the blast furnace is higher than that ofan autothermic process possibilities for lowering the consumption couldbe sought. This would mean that the slope of the process line isreduced. However, it can immediately be seen from the diagram that thiswould only be possible if the point of intersection of the process linewith the ordinate could be shifted upwards as a flatter process linewould otherwise run into the “forbidden zone”. This point ofintersection, however, is fixed by the oxygen demand for precombustionand this in turn results from the heat demand for fusion and the otherprocesses requiring heat in the lower part of the furnace. Since,however, the heat demand in the lower part of the furnace can only bereduced very slightly the process line can only be a little flatterwithout encroaching on the “forbidden zone” and hence the carbonconsumption also can only be lowered by a small amount. Of course, thisconsideration does not exclude the substitution of carbon by otherreducing agents.

Thus, in comparison with an autothermic process the higher carbon demandof the blast furnace and the chemical energy present in the furnace gasremain. The diagram shows that the CO/CO₂ ratio is 3/2. ⅓of the furnacegas is burnt (afterburning) and after transfer through a regenerator theenergy is reintroduced in the form of sensible heat to the combustionair by the tuyeres. ⅔of the furnace gas leave the process withapproximately 20% of the energy introduced in the form of coke.

The discussion of the blast furnace method has shown that althoughprecombustion of the carbon is straightforward in technological terms itresults in a position of the process line close to the “forbidden zone”.Accordingly, the lowest possible slope of the process line and hence thelowest possible carbon consumption cannot be achieved with this method.

The methods can be divided into slow and rapid reduction processes inwhich the residence time of the charged material amounts to severalhours. Processes in a blast furnace and in a rotary-tube furnace inwhich reduction and combustion to produce heat take place in the samechamber are considered to be slow reduction processes.

The Kinglor-Metor process and the Hoganes process have been proposed asslow autothermic reduction processes. In these processes a precombustionstep takes place outside of the reduction chamber. The disadvantage ofthis method, however, is the low efficiency of the transfer of the heatproduced by combustion back into the reduction chamber by thermalconduction. In this case the heat must first of all flow through aceramic wall and then be conveyed onwards within the reactor byconvection in an almost stagnant gas. In another proposal (DE 39 28 415A1) heat transfer from an external combustion chamber is effected via aheating duct system. On account of this slow type of heat transport thespecific efficiencies of these process are low.

Rapid reduction processes are processes in which the residence time ofthe charged material is less than one hour, operations being conductedat elevated temperatures.

These processes include the Festmet process and the Inmetco process inwhich combustion takes place in the same chamber as reduction but bothreactions proceed far apart from one another. It is intended in thismanner that the two gas zones should mix as little as possible. The heatis transferred by radiation from the fire-resistant material in thecombustion chamber heated by the combustion reaction into the reductionchamber, there being better heat transfer to the reduction chamber ofthe coal gasification. On account of the spatial conditions combustioncannot be carried on to complete conversion of CO to CO₂. Thus, theseprocesses cannot be autothermic. Considerable excess energy is carriedaway out of the system.

The aim of the present invention is to provide a method for theextraction of iron by direct reduction of iron ore and a device for thispurpose, the intention being that the process should be largelyautothermic and accordingly should have a minimum specific coalconsumption and energy consumption and that the reduction process shouldbe rapid and capable of being carried out at a high temperature with theresult that there is a high level of conversion of ore to metal.

This task is solved according to the invention by the characterisingcharacteristics of the main claim and the coordinated claim inassociation with their introductory parts.

The use of a separate reduction zone and combustion zone for producingthe necessary enthalpy of reduction for the gasification of the coal andthe reduction of the iron allows a largely autothermic process in whichthe lowest possible amount of carbon is employed for reducing the iron.In the combustion chamber the carbon monoxide produced over and abovethat needed for reduction in the gasification of the coal is burnt andthe heat liberated in doing so is transferred via a high-temperatureheat exchanger to gas from the reduction chamber. A substantialimprovement relative to the state of the art is the forced circulationof gas from the reduction chamber then through the heat exchanger andback into the reduction chamber as a result of which extremely efficienttransfer of heat to the coal to be gasified and the iron ore to bereduced is effected. By using a high-temperature heat exchanger, that isa regenerator, in combination with the forced circulation of thereducing gas an autothermic direct reduction process of high specificefficiency is produced with which the throughput time for ores islowered from hours to minutes.

According to the invention the heat is transferred by rapidly flowinggas to the ore/coal/pellets and, moreover, heat transfer takes place athigh temperatures as a result of which the reduction time in the regionof the rapid reduction process drops and can be lowered to 10 to 15minutes. The degree of conversion of the ore to metal rises to over 90%.

By means of the measures specified in the subsidiary claims advantageousrefinements and improvements are possible.

For the forced circulation it is suitable to use a fan, for example,which is connected to the heat exchanger and circulates the reducinggases through the heat exchanger. This is particularly advantageous whenbefore they are conveyed through the heat exchanger and the fan thereducing gases are cooled by a cooler to temperatures of less than 300°C., for example, so that conventional fans can be used.

It is particularly advantageous to use a plurality of heat exchangersconstructed as regenerators through each of which the hot combustiongases flow for a time, for example, and which are heated up after whichthe reducing gases previously cooled to 300° C. are then conveyedthrough the same regenerator. With the aid of suitable valve connectionsthe heat of the combustion gases can be transferred particularlyadvantageously to the reducing gases by means of a cyclic sequence ofheating and cooling processes of the regenerator or regenerators, onlyinsubstantial quantities of oxygen passing from the waste gases into thereducing gases.

If four regenerators are employed simultaneously the essential heatexchange processes can be carried out synchronously for differentspatial regions of the reduction chamber and in this way a particularlyeffective and rapid reduction of the iron can be achieved. Thecorresponding four steps for the optimum utilisation of the heatproduced in the afterburning of the reducing gases are as follows.

a) Hot gas is drawn in from the combustion chamber by a regenerator andconveyed on to a waste gas unit. In doing so the combustion gas coolsand the regenerator absorbs heat.

b) Cooled reducing gas is blown through the heated regenerator andheated to the working temperature of the reduction reactor. This heatedreducing gas is blown back into the reducing chamber and in this waycarries the required enthalpy of reaction to the coal and the iron ore.

c) This regenerator is cooled further by passing ambient air at roomtemperature through it and passing it on to the combustion chamber. Indoing so the cold ambient air containing oxygen is preheated and thiscontributes to an improvement in the energy balance.

d) Gas is sucked out of the reduction chamber and through theregenerator which has now cooled almost to ambient temperature as aresult of which it is strongly cooled. This cooled gas can then bepassed on to a regenerator which carries out the step described underb).

It can immediately be seen that by using four regeneratorssimultaneously a four-phase process optimised in terms of time andenergy can be carried out. Further variations of this method are alsoconceivable, for example the use of more or fewer regenerators, eg bydispensing with the preheating of the combustion air.

The method according to the invention and the device according to theinvention are employed with particular advantage in a rotary-tubefurnace.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the method according to the invention and the deviceaccording to the invention are described below. These show:

FIG. 1 a RIST diagram;

FIG. 2 a schematic illustration of a plant for carrying out the methodaccording to the invention;

FIG. 3 a schematic illustration of the four-phase process according tothe invention with four regenerators; and

FIG. 4 the energy balance of a four-phase process according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the reduction of iron ore using coal the carbon and the otheroxidisable constituents of the coal have two tasks:

1. a portion of them takes over the oxygen bonded to the iron in the ore(reduction);

2. the remainder reacts with free oxygen (usually from the air) in orderto release the necessary enthalpy of reaction for the reduction reactionor the coal gasification reaction.

The two processes A and B are described stoichiometrically as follows.

A. Reduction with Carbon

Reduction of FeO (haematite) to Fe and conversion of 1.5 CO to 1.5 CO₂

FeO1.5+1.5 CO=Fe+1.5 CO₂  1.

Reaction of half of the resultant CO₂ with C (carbon gasification) toform 1.5 CO.

0.75 CO₂+0.75 C=1.5 CO.  2.

Thus according to equation 2 the quantity of CO needed for the reactionaccording to equation 1 is produced.

The overall equation for 1 and 2 is

FeO1.5+0.75 C=Fe+0.75 CO₂+118 MJ/kmol.  3.

The reduction reaction according to equation 3 is not possible withoutconstraints. On account of thermodynamic limits 10% of carbon monoxidemust still be present in the consumed reduction gas in order for thereduction to proceed. This gives rise to a somewhat higher carbondemand. This is unimportant, however, for the general view. Thecalculations further on take all special thermodynamic features intoconsideration.

The following equation shows a further possibility for reduction bymeans of carbon:

FeO1.5+1.5 C=Fe+1.5 CO+247 MJ/Fe.  4.

In order for the reduction with 1.5 C to proceed 247 MJ/Fe must besupplied to the reduction reactor compared with 118 MJ/Fe for reaction3. In the industrial application a process results which operatesbetween 3 and 4 but is closer to 4. In the autothermic method accordingto the invention both processes need the same amount of carbon but theheat to be transported across the system limits of the reduction andgasification reactor is different.

B. Combustion Reaction of Carbon or Carbon Monoxide with Free Oxygen

The combustion reaction can start from carbon:

x C+x O₂=CO²⁻ x′395 MJ/kmol  5.

or in the case of coal gasification according to Eq 2

or 4 CO formed in excess is burnt:

y CO+y 1/2 O₂ =y CO₂ −y′ 284 MJ/kmol.  6.

In the invention presented here the lowest values thermodynamicallypossible for x and y are achieved and, accordingly, the lowest possibleinput of fossil fuels is needed as energy.

In the method according to the invention the stream of materialsresulting from the reaction of the oxygen of the ore with C, CO or H₂ isphysically separated from the stream of materials emerging from thereaction of the free oxygen with C, CO or H₂.

In the transfer of the enthalpy required for the coal gasification andthe reduction reaction using a heat exchanger it has to be taken intoconsideration that the coal gasification and the reduction of the ironoxides preferably proceed at solids temperatures of over 800° C. Onaccount of the low specific heat of the gases the gas used asheat-transfer medium must be heated to the highest possible temperature,eg 1300° C., in order to transfer the considerable amount of heatrequired per ton of iron without the volume of gas to be circulatedbecoming too great. Since the usable enthalpy reserve of theheat-supplying gas is already exhausted at approximately 800° C. the gasmust be withdrawn at this temperature from the reduction/gasificationzone and be conveyed by a fan through a high-temperature heat exchangeror regenerator heated to approximately 1300° C. There is no fan whichcan assume this task for long periods. Accordingly, the gas drawn off at800° C. must give off its enthalpy down to approximately 300° C. to aregenerator. The gas cooled in this way can now be conveyed withoutdifficulty by a fan and be heated to 1300° C. by another heatedregenerator.

In FIG. 2 a schematic illustration of a plant for the rapid reduction ofiron ore using coal under high-temperature conditions is shown which hasa reduction reactor 10 constructed, for example, in the form of arotary-tube reactor to which ore and coal are fed in a manner which isnot illustrated. In FIG. 2 a bed 11 of ore/coal/pellets on a rotarygrate or the like is shown. Recycling gas having a temperature above theinitiation temperature of the Boudouard reaction (typically <950°C.) iscarried into the reduction reactor 10. There a portion of the ore oxygenis reduced by reaction with the gas (indirect reduction) and furthermoreby transfer from gas to coal the production of CO from CO₂ and C inaccordance with the Boudouard reaction is brought about. The resultingCO reacts with ore oxygen (direct reduction) CO₂ being once moreproduced.

The reducing gas cooled to less than 900° C. is sucked by means of a fan14 from the reduction reactor 10 via a combination of two heatexchangers 12, 13 or recuperators and flows through the fan 14 atapproximately 300° C. The heat exchanger 12 gives the stored heat backto the gas after it emerges from the fan 14.

The plant further has two regenerators 15, 16 possessing heat storagemembers, ceramic spheres for example. Allocated to the regenerators 15,16 are combustion chambers 17, 18 to which air is supplied via a fan 19for the combustion of the reducing gas present in excess. Of course itis also possible to provide just one combustion chamber and this couldbe at a different position. For purposes of preheating the air isconveyed through the recuperator 13. The pipe system carrying thereducing gases is connected via valves 9, 9′ and 4, 5 to theregenerators 15 and 16 and the combustion chambers 17 and 18. The airfor the combustion chambers 17, 18 is conveyed from the recuperator 13via valves 3, 6. The regenerators 15, 16 are further connected viavalves 7, 8 to a waste gas pipe 20 and connected via valves 1 and 2 tothe reduction reactor 10. The regenerators 15, 16 assume two states. Instate one the valves 2, 3, 4, 7, 9′ are closed while the valves 1, 5, 6,9 are open. Approximately 80-90% of the reducing gas or recycling gasarrives in the regenerator 15 which gives up heat so that the recyclinggas is heated to a temperature <1000° C., for example approximately1300° C., and is fed back into the reduction chamber 10. The remainingportion (10-20%) of the reducing gas flows into the combustion chamber18 in which it is burnt with the air and the heat produced heats theregenerator 16. The waste gas, in which both the ore oxygen as well asthe oxygen coming from combustion leave the system, is carried off viathe waste gas pipe 20. However, under no circumstances is combustion gasmixed with gas which is conveyed through the reduction reactor. In state2 the regenerator 15 takes up heat produced by combustion in thecombustion chamber 17 and the regenerator 16 gives up its heat to thereducing gas which is under forced circulation. In doing so the valves2, 3, 4, 7 and 9′ are open while the valves 1, 5, 6 and 8 are closed.

In FIG. 3 the scheme of four cyclically operating regeneratorsinterconnected to form a set is shown. FIG. 3 shows how the fourregenerators R1, R2, R3, R4 work together during the course of thefour-phase cycle. Each regenerator R1, R2, R3 and R4 passes through thesame sequence of four cycles Z1 to Z4. The figures given relate to theproduction of one ton of iron in the form of DRI. The conditions arepresented as though the entire heat exchange for the production of thisquantity of iron went through only one set of four heat exchangers. In aproduction plant having an annual capacity of 500,000 t of Fe pa one tonof iron is produced approximately every minute. It is then necessary toemploy a whole series of such sets each comprising four regenerators onthe reduction reactor. Rotary grate or travelling grate methods areparticularly suitable for arranging a series of sets of regeneratorsalong the reduction pathway and the pathway of the coal gasificationproceeding at the same time. If for a plant of the aforesaid capacitytwelve sets of regenerators are assumed in which each of the fourregenerators has a refractory charge of 2 t for a changeover time of oneminute the throughput figures specified in FIG. 3 are to be divided by12 to obtain the values for one regenerator set.

FIG. 3 shows the four regenerators in one of four states Z1 to Z4.Regenerator R1 is in state Z1 and is just being acted upon by the hotburner gases (see lower lines of text). In doing so 560 sm3 of gascontaining 92% CO/8% CO₂ are burnt with 1280 sm3 of air. Gas and airhave admission temperatures of 800° C. and 900° C. respectively. Sincethe combustion gases would be too hot for regenerator R1 the combustiongases are mixed with 1600 sm3 of circulating waste gas at 250° C. Inthis state, therefore, the regenerator takes up 8.11 GJ.

Regenerator R2 is in state Z2 and as an intermediate accumulator ittakes heat from the 8240 sm3 of process gas removed from the reductionreactor. The gas is cooled down from 800° C. to 300° C. so that it canbe circulated by a fan G1. In doing so 6.5 GJ are given up to theregenerator R2.

The fan G1 conveys the gas cooled in R2 to be heated to the workingtemperature of 1300° C by regenerator R3 which is in state Z3. In thecourse of being heated the process gas removes 13.01 GJ from theregenerator. Due to the regeneration process the gas now has an enthalpyreserve of 6.5 1 GJ. This is the enthalpy requirement for a ton of ironproduced by the reaction sequence A in FIG. 3 (363 MJ/Fe corresponds to6.5 1 GJ/t Fe).

In state Z4 the regenerator R4 heats the combustion air for regeneratorR1 to 900 ° C. using the enthalpy still left after the process gas hasbeen heated. In doing so 1.61 GJ are withdrawn.

In the mode of operation described the heat balance of the regeneratorsystem is balanced out. The process is autothermic and needs the lowestpossible amount of coal. This is just sufficient to cover the reductionof the oxides and the other energy inputs still required: drying,calcining and sensible heat of the matrix and the iron. It was assumedfor these that they would leave the reactor at 1150° C. In addition, acertain thermal loss and the enthalpy contained in the waste gas leavingthe plant at 250° C. were taken into account.

The carbon demand can, however, be lowered further if the energy contentof the coking gases from the coal, approximately 200 sm3/t of coalcontaining approximately 34 MJ/sm3, are utilised.

As FIG. 4 shows and as mentioned also in connection with equations 3 and4, there are different possibilities for conducting an autothermicprocess while the carbon demand remains the same. These variants can allbe carried out by the method according to the invention.

Section 1 in FIG. 4 shows the enthalpy demand (414 MJ/Fe) required forthe breakdown (dissociation) of the iron oxide. Together with theenthalpy demand required for other things of 135 MJ/Fe this yields anoverall demand of 549 MJ/Fe. In order to answer the question as to howmuch carbon is required to provide this enthalpy it is calculated howmuch carbon oxidised to CO₂ liberates this enthalpy. Section 2 of FIG. 4shows that 1.39 mol of C is needed for this. Section 3 of FIG. 4 nowshows what proportion of this 414 MJ/Fe or 549 MJ/Fe needed to preparethe iron must be transferred from the outside into the reduction orgasification reactor so that the reduction can run mainly via CO. Of thenecessary 540 MJ/Fe, 363 MJ/Fe must be supplied from the outside. Theyare liberated by burning the CO produced in the reduction reaction inthe combustion zone of the reactor and are transferred via regenerators.

The reduction illustrated in Section 4 of FIG. 4 also requires 549 MJ/Feagain but only 253 MJ/Fe must be transferred. The carbon demand for thereduction and further carbon for combustion occurring outside thereduction chamber amounts as in Section 3 of FIG. 4 to a total of 1.39mol of C/Fe. As mentioned earlier, however, the reaction of Section 4must be shifted slightly towards 3 to clear the thermodynamic hurdle.Thus in addition to the CO₂ approximately 10% of CO must be present inthe waste gas.

An important conclusion of this examination of different reactionpathways for the same carbon demand is that for processes close to “4”less heat must be transferred through the regenerators into thereduction chamber. Since, however, the performance of a coal reductionreactor depends on the efficiency of the heat transfer, the throughputof a given plant can be raised by shifting the process from “3” to “4”by approximately 20%.

What is claimed is:
 1. A method for the extraction of iron by directreduction of iron ore using coal in a reduction reactor withoutadditional reducing gas, comprising the steps of: gasifying the coal inthe reactor together with the carbon dioxide produced during reductionto form iron, reducing gas and excess reducing gas; burning excessreducing gas in a combustion zone separated from the reduction zone ofthe reactor; feeding back the heat produced via a heat exchanger to thegas present in the reduction chamber of the reactor to cover theenthalpy demand of the reactions taking place in the chamber;constructing the heat exchanger as a high-temperature heat exchanger;and circulating the gas from the reduction chamber by forced circulationthrough the heat exchanger and into the reduction chamber to improve theheat transfer to the iron ore and the coal.
 2. The method according toclaim 1, further comprising the steps of: burning a portion of the gasconveyed out of the reduction chamber and storing the heat produced andabsorbing the heat stored in the combustion process by the other portionof the gas conveyed out of the reduction chamber; and then feeding backthe heat with the other portion of gas into the reduction chamber. 3.The method according to claim 1 further comprising the steps of: coolingthe reducing gas after emerging from the reduction chamber; storing theheat produced during cooling temporarily; and conveying the cooled gasvia forced circulation means before the cooled gas absorbs the heatproduced in the combustion process.
 4. The method according to claim 3,further comprising the step of: using at least one part of thetemporarily stored heat for heating one of the air needed for thecombustion process and the oxygen needed for the combustion process. 5.The method according to claim 1, further comprising the step of:carrying out the coal gasification and the iron reduction in immediatespatial proximity.
 6. The method according to claim 1, furthercomprising the step of: mixing the coal and the ore with one anotherprior to gasification and reduction.
 7. The method for extraction ofiron by direct reduction of iron ores using coal, the step comprising:using a reduction chamber for the gasification of coal and the reductionof the ore to form iron; connecting a combustion chamber to thereduction chamber; forming some reducing gas and forming some excess gasnot required for the reduction during gasification; extensivelycombusting the excess gas in the combustion chamber, returning the heatproduced during combustion with the aid of at least one heat exchanger,said heat exchanger constructed as a regenerator having a storage mass;storing the heat produced during combustion in the storage mass; andconnecting a means of force circulation to the reduction chamber and theheat exchanger for the circulation of the reducing gas through thereduction chamber and the heat exchanger.
 8. The method of claim 7further comprising the steps of: conveying hot gas from the combustionchamber through a first regenerator thereby cooling the hot gas and thenpassing it on to a waste gas unit.
 9. The method of claim 8 furthercomprising the steps of: conveying cooled reducing gas through a secondregenerator and thereby heating the cooled reducing gas to an operatingtemperature of the reduction chamber and then blowing the heatedreducing gas into the reduction chamber.
 10. The method of claim 9further comprising the steps of: conveying ambient air at approximatelyroom temperature through a third regenerator, heating up the ambient airand then conveying the heated ambient air into the combustion chamber.11. The method of claim 10 further comprising the steps of: sucking thegas from the reduction chamber via a fan through a fourth regeneratorand then heating the gas from the reduction chamber through the secondregenerator to the operating temperature of the reduction chamber andthen blowing the heated gas into the reduction chamber.
 12. The methodof claim 7 further comprising the steps of: providing four generators,wherein each regenerator exhibits the following steps one after theother: conveying hot gas from the combustion chamber through the firstregenerator thereby cooling the hot gas and then passing it on to awaste gas unit; conveying cooled reducing gas through the secondregenerator and thereby heating the cooled reducing gas to an operatingtemperature of the reduction chamber and then blowing the heatedreducing gas into the reduction chamber; conveying ambient air atapproximately room temperature through the third regenerator, heating upthe ambient air and then conveying the heated ambient air into thecombustion chamber, and sucking the gas from the reduction chamber via afan through the fourth regenerator and then heating the gas from thereduction chamber through the second regenerator to the operatingtemperature of the reduction chamber and then blowing the heated gasinto the reduction chamber.